1. Field of the Invention
The present invention relates to an electronic endoscope system that is capable of displaying a normal color image obtained by using a normal lamp emitting visible light, such as a xenon lamp, and an auto-fluorescent image for observing or diagnosing a lesion, such as a cancer. In particular, it relates to a display process for simultaneously displaying an auto-fluorescent image and a normal color image on a monitor.
2. Description of the Related Art
In an electronic endoscope system with an auto-fluorescent observation function, light, having a wavelength in the ultraviolet range or in that vicinity (hereinafter, called “excitation-light”), is emitted toward the epithelium of an organ such as the lungs. Tissue in the epithelial layer has a fluorescent substance, which emits fluorescent light (hereinafter, called “auto-fluorescent light”) when the excitation-light is illuminated thereon. An object image is formed on an image sensor provided on a tip portion of a video-scope, due to the fluorescent light passing through an objective lens, so that an image based on fluorescent light (hereinafter, called an “auto-fluorescent image”) is displayed on a monitor. Since the amount of auto-fluorescent light, which is emitted from a lesion or a piece of abnormal tissue, is weak compared to that emitted from the normal tissue, luminance of the lesion or the area adjacent to the lesion in an auto-fluorescent image is relatively small; thus, the lesion can be easily detected compared with a normal full color image obtained by white light emitted from a lamp such as a xenon lamp.
For example, consider a first image sensor for white light and a second image sensor for auto-fluorescent light which are equipped with the electronic endoscope simultaneously to display the normal color image and the auto-fluorescent image. Also, in the case of an electronic endoscope having one image sensor, white light and excitation-light are alternately emitted to simultaneously display the normal color image and the auto-fluorescent image. Further, to distinguish a lesion from a normal tissue, an image in which the lesion portion is colored (hereinafter, called a “pseudo-color image”) is generated on the basis of the normal color image and the auto-fluorescent image. When displaying the pseudo-color image, a switch button provided on a video-scope or a video-processor is switched so that the normal image and/or the auto-fluorescent image are erased and the pseudo-color image is displayed.